A number of publications describe catalytic carrier structures in which the overheating of the catalytic coatings is reduced by limiting the maximum heterogeneous fuel conversion to approximately 50%. This is achieved by providing the channels arranged inside the catalyzer alternately with a catalytic coating, i.e. coated and non-coated channels are alternated (cf. U.S. Pat. No. 4,870,824 or U.S. Pat. No. 5,346,389 or U.S. Pat. No. 5,328,359). In the solutions described in U.S. Pat. No. 5,346,389 or U.S. Pat. No. 5,328,359, either an alternately coated, corrugated carrier sheet is folded in zigzag shape, or a structure of two superposed sheets is rolled up. U.S. Pat. No. 5,518,697 or U.S. Pat. No. 5,512,250 furthermore disclose a three-layer structure in which the coated and uncoated channels have different dimensions in order to further improve the cooling of the catalytic coatings.
In order to prevent a deactivation of the catalytic coatings, it is critical that their surface temperature is maintained below a predetermined value that depends on the type of the catalyzer material. For example, in the case of PdO, a reduction to Partial diffuser sets in at temperatures above approximately 900° C. (at pressures >15 bar). In the above-mentioned publications, the surface temperature is limited in that not all surfaces are provided with a catalytic coating. In U.S. Pat. No. 5,328,359, the surface temperature remains high under the operating conditions of a gas turbine: Tsurface=Tin+½Tad typically reaches 1,000° C., whereby Tsurface is the surface temperature, Tin is the temperature at the inlet of the catalyzer, and Tad is the adiabatic combustion temperature. In U.S. Pat. No. 5,518,697, additional convective cooling is achieved by enlarging the cross-section surfaces of the non-coated channels in relation to the coated channels. In both cases, however, channels exist that are not provided with any sort of catalytic coating. Under the conditions present with a gas turbine (mixtures with λ=2.2 at pressures >15 bar), there exists, however, the concrete risk of homogeneous ignition near the surfaces, particularly in the uncoated channels, since no reduction of the fuel concentration occurs there. This problem is increased in that the uncoated channels at the same time are those channels with the greatest hydraulic diameter.